1. Field of the Invention
The present invention relates to a printing apparatus such as a typewriter or printer having a tabulator/margin setting device for tabulation or margin setting, and more particularly to such apparatus capable of controlling the printing operation in response to the tabulation or margin set positions of said device identified by the open/closed state of switch means.
2. Description of the Prior Art
Conventional typewriters are provided with left-right margin setting bars which can be set at arbitrary positions for selected desired print start and end positions. Also already known in such typewriters is a tabulator device for conducting a spacing function without printing operation in the spaces wherein the printing operation is not required between the left- and right-end positions.
In conventional typewriters said margin setting bars, being generally positioned in the front side of the typewriter, are easily manipulated and allow visual confirmation of the margin set positions in relation to the current printing position. On the other hand the conventional tabulator device is defective in that the set positions for tabulation cannot be visually recognized but can only be confirmed when the carriage bearing the printing means or the platen bearing the recording paper is stopped at one of said set positions after a spacing function. This defect is due to the difficulty of placing a mechanical tabulator device in the front side of the typewriter.
Also tabulator setting in conventional typewriters requires a three-step operation of displacing the carriage, stopping the carriage at a desired set position and actuating a tabulator setting key in the keyboard. In addition such tabulator setting can be cleared only for each set position by actuating a tabulator key to displace the carriage to said set position and actuating a tabulator clear key, so that plural tabulation set positions need to be cleared by the repetition of the above-mentioned procedure for each set position.
Such known tabulator/margin setting devices rely on mechanical control through plural levers for setting or clearing of the tabulator or margin positions and are inevitably associated with insufficient reliability. In order to avoid such drawbacks there has been proposed the use of electronic components in place of mechanical parts for improving the reliability and achieving multiple functions. The so-called electronic tabulator utilizing electronic control performs the tabulation or margin-setting functions through the comparison of the current carriage position with the tabulation or margin set positions previously stored in an electronic memory, and provides a simpler structure and a higher reliability in comparison with the conventional mechanical tabulator/margin-setter. However such an electronic tabulator is still defective in that the data of tabulation or margin set positions stored in a destructable memory are lost when the power supply is interrupted, and this defect can only be prevented by the use of an expensive nondestructable memory.